Multicolour tunable luminescence of thermal-stable Ce3+/Tb3+/Eu3+-triactivated Ca3Gd(GaO)3(BO3)4 phosphors via Ce3+ → Tb3+ → Eu3+ energy transfer for near-UV WLEDs applications

A series of single-component blue, green and red phosphors have been fabricated based on the Ca₃Gd(GaO)₃(BO₃)₄ host through doping of the Ce³⁺/Tb³⁺/Eu³⁺ ions, and their crystal structure and photoluminescence properties have been discussed in detail. A terbium bridge model via Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer has been studied. The emission colours of the phosphors can be tuned from blue (0.1661, 0.0686) to green (0.3263, 0.4791) and eventually to red (0.5284, 0.4040) under a single 344 nm UV excitation as the result of the Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer. The energy transfer mechanisms of Ce³⁺ → Tb³⁺ and Tb³⁺ → Eu³⁺ were found to be dipole-dipole interactions. Importantly, Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors had high internal quantum efficiency. Moreover, the study on the temperature-dependent emission spectra revealed that the Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors possessed good thermal stability. The above results indicate that the phosphors can be applied into white light-emitting diodes as single-component multi-colour phosphors.     

Luminescent properties of a novel afterglow phosphor Sr3Al2O5Cl2:Eu,Ce

A series of Eu²⁺ and Ce³⁺ doped/co-doped Sr₃Al₂O₅Cl₂ afterglow phosphors that presented various bright colors were successfully synthesized via high temperature solid state reaction. The structure and luminescence properties of the obtained samples were characterized by X-ray powder diffraction (XRD), photoluminescence (PL) spectra and decay curves as well as the thermoluminescence (TL) glow curves. The XRD results showed that all the phase could be indexed to the orthorhombic structure with the space group P2₁2₁2₁. After being exposed to a 254 nm or 365 nm mercury lamp, blue/yellow-orange afterglow emissions with broad bands peaking around 620 nm/435 nm, which were ascribed to the characteristic 4f⁶5d–4f⁷/5d¹–4f¹ transitions of Eu²⁺/Ce³⁺, could be observed in phosphors of Sr₃Al₂O₅Cl₂:Eu²⁺/Sr₃Al₂O₅Cl₂:Ce³⁺, respectively. Because of the overlap spectral range between the Sr₃Al₂O₅Cl₂:Eu²⁺ and Sr₃Al₂O₅Cl₂:Ce³⁺ phosphors, the energy transfer (ET) from Ce³⁺ to Eu²⁺ occurred. The related ET process was discussed in detail. Moreover, the incorporation of Ce³⁺ could significantly prolong the afterglow duration of Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor, which was due to the increase of trap concentration. Consequently, 6 h of the afterglow duration could be observed in Sr₃Al₂O₅Cl₂:1.0%Eu²⁺, 0.5%Ce³⁺ sample, exhibiting much longer than that of Sr₃Al₂O₅Cl₂: 1.0%Eu²⁺ (3 h). From the afterglow decay curves and the fitting results, the optimal concentration of Ce³⁺ for the enhanced afterglow property was experimentally determined to be 0.5%.     

Tunable luminescence and energy transfer properties of MgY4Si3O13: Ce3+, Tb3+, Eu3+ phosphors

The tricolor-emitting MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors for ultraviolet-LED have been prepared via a high-temperature solid-state method. X-ray diffraction, photoluminescence emission, excitation spectra and fluorescence lifetime were utilized to characterize the structure and the properties of synthesized samples. Two different lattice sites for Ce³⁺ are occupied from the host structure and the normalized PL and PLE spectra. The emissions of single-doped Ce³⁺/Tb³⁺/Eu³⁺ are located in blue, green and red region, respectively. The energy transfer from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ has been validated by spectra and decay curves and the energy transfer mode from Tb³⁺ to Eu³⁺ was calculated to be electric dipole-dipole interactions. By adjusting the content of Tb³⁺ and Eu³⁺ in MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺, the CIE coordinates can be changed from blue to green and eventually generate white light under UV excitation. All the results indicate that the MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors are potential candidates in the application of UV-WLEDs.     

Facile synthesis and spectroscopic characterization of siliconitride phosphors for white light‐emitting diodes

A modified chemical vapor deposition (CVD) technique is used to synthesize the color‐tunable siliconitride Sr_2‐1.5x‐yCe_xEu_ySi₅N₈ (x = 0.000‐0.016 and y = 0.000‐0.020) phosphors. In comparison with the conventional solid‐state method, the CVD approach successfully improved the crystallinity, particle size distribution, and photoluminescence through the enhanced gas‐solid reaction. Under blue excitation, Sr_1.98Eu_0.02Si₅N₈ exhibited a red emission band at 618 nm. The incorporation of Ce³⁺ ions increased the emission intensity of Eu²⁺ ions by approximately 10% owing to the enhanced absorption and dipole‐dipole energy transfer process from Ce³⁺ to Eu²⁺ ions. It resulted in a shift of the emission colors from yellow to red region. The external and internal quantum efficiencies of Sr_1.906Ce_0.06Eu_0.004Si₅N₈ were calculated as 54% and 70%, respectively. The activation energy of thermal stability for Sr_1.906Ce_0.06Eu_0.004Si₅N₈ was evaluated as 0.31 eV. A white LED with a color rendering index of 80 and a CCT of 4964 K was successfully fabricated with the present phosphors. The current research demonstrated a new series of Sr₂Si₅N₈:Ce³⁺, Eu²⁺ phosphors with color‐tunability for fabricating white LEDs with high color‐rendering index.     

A single‐phase,thermally stable and color-tunable white light emitting Na2Ca1-x-yCexMnyP2O7 phosphors for white light emitting diodes via energy transfer

The solid-state reaction method was used to develop a series of Na₂Ca_1-x-yCe_xMn_yP₂O₇ phosphors in an H₂–N₂ environment. The crystal structure of the pyrophosphate host, valence state of dopants (Ce, Mn), emission behavior of dopants, energy transfer mechanism, and thermal quenching behavior were thoroughly examined. Doping with Ce³⁺ and Mn²⁺ ions enhanced the photoluminescence characteristics of Na₂Ca_1-x-yCe_xMn_yP₂O₇ while having negligible effect on the host's phase purity. Under 365 nm UV light irradiation, the addition of Ce³⁺ ion in the Na₂CaP₂O₇ host revealed an asymmetric band with the typical blue emission around 415 nm and a shoulder around 455 nm. To obtain white light, Mn²⁺ ion was supplementarily substituted to the present system. When the Mn²⁺ ions concentration was elevated in the Na₂CaP₂O₇ host, the emission intensity of 560 nm peak corresponding to Mn²⁺ transition enhanced significantly at the cost of Ce³⁺ emission of 415 nm. The systematic decrease of Ce³⁺ emission intensity and corresponding increase in the Mn²⁺ intensity with the increase in Mn²⁺ concentration indicated the possibility of effective energy transfer from Ce³⁺ to Mn²⁺ ions. The obtained results indicated that energy transfer from the Ce³⁺ to Mn²⁺ ions governed by dipole-quadrupole interaction. Because of the efficient energy transfer, the blue emission from Ce³⁺ and the orange red emission of Mn²⁺ provide white light from a single host along with high value of activation energy and low thermal quenching behaviour make the present phosphors to be suitable for high-power LEDs.     

Fluorescence improvement of Ba1.3Ca0.7SiO4:Eu,Mn phosphors via Dy addition and their color-tunable properties

A series of novel single-phase white phosphors Ba_1.3Ca_0.69−x−ySiO₄:0.01Eu²⁺,xMn²⁺, yDy³⁺ were synthesized by the solid-state method. The excitation spectra of these phosphors exhibit a broad band in the range of 260–410 nm, which can meet the application requirements for near-UV LED chips (excited at 350–410 nm). The emission spectra consist of two broad bands positioned around 455 nm and 596 nm, which are assigned to 5d→4f transition of Eu²⁺, and ⁴T₁→⁶A₁ transition of Mn²⁺, respectively. The luminescence intensity of phosphors enhances obviously by doping Dy³⁺ ions, and the intensity of two bands reaches an optimum when Dy³⁺ amounts to 2 mol%. In addition, thermoluminescence investigation of phosphor was conducted, getting two shallow trap defects with activation energy of 0.43 eV and 0.45 eV, which demonstrates the energy transfer mechanism of Dy–Eu through the process of hole and electron traps. By precisely tuning the Mn²⁺ content, an optimized white light with color rendering index (CRI) of R_a=84.3%, correlated color temperature (CCT) of T_c=8416 K and CIE chromaticity coordinates of (0.2941, 0.2937) is generated. The phosphor could be a potential white phosphors for near-UV light emitting diodes.     

Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

Efficient Near‐Infrared Emission of Ce3+–Nd3+ CoDoped (Sr0.6Ca0.4)3(Al0.6Si0.4)O4.4F0.6 Phosphors for c‐Si Solar Cell

Ce³⁺, Nd³⁺ codoped (Sr_0.6Ca_0.4)₃(Al_0.6Si_0.4)O_4.4F_0.6 phosphors were synthesized through the high‐temperature solid‐state reaction method. Luminescence spectra, absorption spectra, and decay lifetimes of these samples have been measured to prove the energy‐transfer process from Ce³⁺ to Nd³⁺. Under UV and blue light excitation, (Sr_0.6Ca_0.4)₃(Al_0.6Si_0.4)O_4.4F_0.6:Ce³⁺,Nd³⁺ phosphors exhibit near‐infrared (NIR) emission, mainly peaking at 1093 nm and secondarily at 916 nm. The NIR emission matches well with the band gap of c‐Si. Results of this work suggest that the (Sr_0.6Ca_0.4)₃(Al_0.6Si_0.4)O_4.4F_0.6:Ce³⁺, Nd³⁺ phosphors have potential application as down‐shifting luminescent convertor for enhancing the photoelectric conversion efficiency of c‐Si solar cell.     

Synthesis and characterization of Eu3+-doped C12H18Ca3O18 phosphor

A series of Eu³⁺-doped C₁₂H₁₈Ca₃O₁₈ phosphors were synthesized through a facile hydrothermal method and the properties of as-prepared phosphors were explored by X-ray diffractometer (XRD), scanning electron microscope (SEM), and photoluminescence (PL) spectrometer. The exploration results indicated that the C₁₂H₁₈Ca₃O_18:Eu³⁺ had been successfully synthesized. The morphology of C₁₂H₁₈Ca₃O_18:Eu³⁺ was a strip with the size of 100–4000 nm × 50–400 nm × 50–200 nm and the ratio of length to width of 2–80. The strongest emission peak of C₁₂H₁₈Ca₃O_18:Eu³⁺ around 620 nm was ascribed to ⁵D_o→⁷F₂ transition of Eu³⁺, and the peaks centered at 590, 653 and 694 nm respectively corresponded to ⁵D_o →⁷F₁, ⁷F₃, and ⁷F₄ transitions. C₁₂H₁₈Ca₃O_18: Eu³⁺ gave the red light emission, as indicated by color coordinate analysis. The photoluminescence intensity of the phosphors prepared under the Eu³⁺ concentration of 6% was the highest. The crystal structure of C₁₂H₁₈Ca₃O_18:Eu³⁺ was changed after europium ions occupied the lattice position of calcium ions. Europium ion could displace calcium arbitrarily. As a new kind of matrix, calcium citrate possesses the properties of both organic and inorganic compounds and the luminescent C₁₂H₁₈Ca₃O₁₈: x Eu³⁺ particles may be applied in biological fluorescent tags and luminescent materials.     

Energy transfer and color-tunable emission in Ba2Y2Si4O13:Bi3+,Eu3+ phosphors

Single-composition Ba₂Y₂Si₄O₁₃:Bi³⁺,Eu³⁺ (BYSO:Bi³⁺,Eu³⁺) phosphors with color-tunable and white emission were prepared by conventional high temperature solid-state reaction method. The structural and luminescent properties of these phosphors were thoroughly investigated through X-ray diffraction, photoluminescence, and decay curves. BYSO:Bi³⁺ phosphors show two excitation peaks at 342 and 373 nm, and give two emission peaks at 414 and 503 nm, respectively, indicating that there are two sites of Bi³⁺ in BYSO. The energy transfer from Bi³⁺ to Eu³⁺ was investigated in detail. Varied hues from blue (chromaticity coordinate [0.219, 0.350]) to white (0.288, 0.350) and orange-red light (0.644, 0.341) can be generated by adjusting the content of Eu³⁺. Pure white light emission (0.311, 0.338) can be obtained under the excitation of 355 nm in BYSO:3%Bi³⁺,20%Eu³⁺ phosphor. Besides, BYSO:Bi³⁺,Eu³⁺ phosphors exhibit distinct thermal quenching properties, whose emission intensity at 473 K is 82.6% of that at 298 K. Our results indicate that BYSO:Bi³⁺,Eu³⁺ may be applied as conversion phosphors for n-UV-based W-LEDs.     

The electronic structure,site occupancy and luminescent properties of Ce3+-activated Li2Ca2Si2O7 blue phosphor

Rare earth activated lithium-containing alkaline earth silicates is an intensely studied topic in the fields of luminescent materials. In this study, a cerium-activated lithium-silicate blue phosphor, Li₂Ca₂Si₂O₇:Ce³⁺, was explored using structural computational simulations and systematic experiments. The Li₂Ca₂Si₂O₇:Ce³⁺ phosphor can be efficiently excited by near-ultraviolet and cathode ray light sources. According to the spectroscopic redshift theory, time-resolved photoluminescence (TRPL) and cathodoluminescence (CL) spectra, it is determined that the broad emission of Li₂Ca₂Si₂O₇:Ce³⁺ comes from two different luminescent centers. In addition, Li₂Ca₂Si₂O₇:Ce³⁺ exhibits strong blue emission at ~415 nm with high quantum yield and stable emission under high temperature and continuous electron beam bombardment. Therefore, this study provides a new insight into developing new high-efficiency and high-purity trichromatic phosphors.     

Synthesis and photoluminescent properties of high-efficient color-tunable Ba3Y2B6O15: Ce3+, Tb3+ phosphors

High-efficient Ce³⁺/Tb³⁺ co-doped Ba₃Y₂B₆O₁₅ phosphors with multi color-emitting were firstly prepared, and their structural and luminescent properties were studied by XRD Rietveld refinement, emission/excitation spectra, fluorescence lifetimes as well as temperature-variable emission spectra. Upon 365?nm excitation, the characteristic blue Ce³⁺ band along with green Tb³⁺ peaks were simultaneously found in the emission spectra. Moreover, by increasing concentration of Tb³⁺, a blue-to-green tunable emitting color could be realized by effective Ce³⁺→Tb³⁺ energy transfer. Furthermore, all Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ phosphors exhibit high internal quantum efficiency of ~?90%, while the temperature-variable emission spectra reveal that the phosphors possess impressive color stability as well as good thermal stability (T₅₀ =?~?120?°C). The results indicate that these efficient color-tuning Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ might be candidate as converted phosphor for UV-excited light-emitting diodes.     

Solvothermal synthesis of red and green emitting Ca1.65Sr0.35SiO4:Eu and Ca1.65Sr0.35SiO4:Eu phosphors for solid-state lighting applications

A novel and facile synthetic approach has been trialed, and attempted with success in the preparation of two phosphors namely, a red emitting CaSrSiO₄:Eu³⁺ and a green emitting CaSrSiO₄:Eu²⁺. These phosphors were successfully synthesized using a simple co-precipitating solvo-thermal strategy wherein tetraethyl orthosilicate (TEOS) as silica source and the acetate precursors of strontium (Sr²⁺), calcium (Ca²⁺) and europium (Eu³⁺) are utilized. The material so obtained is subjected to an extensive photoluminescence behavior study. The concentration of the dopant (Eu³⁺and Eu²⁺) plays a significant role in the determination of photoluminescence behavior and hence a systematic and in-depth experimental studies were done and the results are synchronized. On interpretation of the output, it came to light that an intense emission signals sparked in the red region (590 and 615 nm) in the case of phosphor doped with Eu³⁺, which is excited under near ultra violet (395 nm) and blue (466 nm) region. In case of the CaSrSiO₄ sample doped with Eu²⁺_, an intense broad green signal (~510 nm) is obtained under the excitation range of 350–430 nm. The results obtained are quite encouraging and made a strong confirmation as, the solvo-thermally synthesized CaSrSiO₄, which is activated by the dopants namely Eu³⁺ and Eu²⁺ possesses an immense potential and it is exactly tapped by the adopted methodology. Despite its strong impact, it will also assure a strong revolution in the fabrication and thus the commercialization of white LEDs as both the red and green emitting phosphor.     

Decay Behavior in Ce3+‐doped La3Si6N11 and Lu3Al5O12 Phosphors

Ce³⁺‐activated light emitting diode (LED) phosphors have been extensively examined for photoluminescence, and have been the focus of many detailed structural studies. However, reports of the decay curves of Ce³⁺‐activated LED phosphors are rare. Although we have reported the decay behaviors of several Eu²⁺‐activated LED phosphors such as Sr₂SiO₄, Sr₂Si₅N₈, and CaAlSiN₃, we have never conducted an in‐depth study into the decay behavior for Ce³⁺‐activated LED phosphors. For this study, we investigated the decay curves of well‐known Ce³⁺‐activated LED phosphors such as La₃Si₆N₁₁ and Lu₃Al₅O₁₂. Similar to Eu²⁺‐activated LED phosphors, the decay behavior of Ce³⁺‐activated LED phosphors was sensitive to the Ce³⁺ concentration and to the detection wavelength. There was active nonradiative energy transfer between the Ce³⁺ activators located at different sites.     

White light emission from Eu co-activated Ca2Gd8Si6O26:Dy nanophosphors by solvothermalsynthesis

Ca₂Gd₈(SiO₄)₆O₂ (CGS) nanophosphors with different concentrations of single-doped Dy³⁺ ions and co-doped Dy³⁺/Eu³⁺ ions were prepared by a solvothermal synthesis. Very fine particles in the nanometer range could be achieved by this method, as evidenced by transmission electron microscope measurements. The hexagonal phase of the oxyapatite structure was confirmed by X-ray diffraction patterns. The energy transfer between Eu³⁺ and Dy³⁺ ions was investigated by photoluminescence excitation and emission properties. These phosphors had absorption bands in the UV and NUV region, which are suitable for the emission wavelength of UV or NUV light-emitting diodes (LEDs). With increasing the Eu³⁺ ion concentration, the emission peak intensity corresponding to the ⁵D₀→⁷F₂ transition increased and the yellow (⁴F_9/2→⁶H_13/2) emission intensity also increased compared to the blue (⁴F_9/2→⁶H_15/2) emission intensity due to the increased energy transfer between Dy³⁺ to Eu³⁺ ions. Thus, the Eu³⁺ ions compensated the red emission component of the Dy³⁺ doped CGS nanophosphors. Such phosphors are expected to have potential applications for NUV based white LEDs.     

Synthesis,structure and luminescent properties of Eu3+ doped Ca3LiMgV3O12 color-tunable phosphor

A new vanadate Ca₃LiMgV₃O₁₂ and its Eu³⁺-doped counterparts were synthesized. Rietveld confinement result of Ca₃LiMgV₃O₁₂ host indicates that it belongs to cubic space group Ia-3d with parameters of a =?12.4300?Å, V =?1920.49?ų, Z?=?8. Under UV excitation, pure Ca₃LiMgV₃O₁₂ exhibits a bluish-green broadband emission at 490?nm, while Eu³⁺ doped Ca₃LiMgV₃O₁₂ shows one bluish-green broad band with a series of red sharp peaks, which originate from the V⁵⁺-O^2- charge transfer and the Eu³⁺ intra-4f transitions, respectively. The occurrence of VO₄→Eu³⁺ energy transfer is confirmed by decay lifetime analysis and time-resolved emission spectra. It is found that emitting color varies from bluish-green to orange-red with increasing Eu³⁺ concentration. VO₄ bluish-green and Eu³⁺ red emission shows different thermal quenching response with increasing temperature, due to their different activation energy.     

Tuning the Color Emission of Sr2P2O7: Tb3+, Eu3+ Phosphors Based on Energy Transfer

A series of color tunable Tb³⁺‐ and Eu³⁺‐activated Sr₂P₂O₇ phosphors were synthesized by a traditional solid‐state reaction method in air atmosphere. The crystal structure, photoluminescence (PL) properties, energy transfer, thermal stability, and luminous efficiency were investigated. A series of characteristic emission of Tb³⁺ and Eu³⁺ were observed in the PL spectra and the variation in the emission intensities of the three emission peaks at around 416 nm (blue), 545 nm (green), and 593 nm (orange‐red) induced the multicolor emission evolution by tuning the Tb³⁺/Eu³⁺ content ratio. The energy‐transfer mechanism from Tb³⁺ to Eu³⁺ ion was determined to be dipole–dipole interaction, and the energy‐transfer efficiency was about 90%. The novel phosphors have excellent thermal stability in the temperature range of 77–473 K and the Commission International De L'Eclairage 1931 chromaticity coordinates of Sr₂P₂O₇: Tb³⁺, Eu³⁺ (λ_ex = 378 nm) move toward the ideal white light coordinates.     

Tunable Emission Phosphor Ca4Y6O(SiO4)6:Ce3+, Eu2+: Luminescence and Energy Transfer

A series of Ca_4–yY_6–xO(SiO₄)₆: xCe³⁺, yEu²⁺ samples are synthesized by a high‐temperature solid‐state method. Under 356 nm excitation, Ca₄Y₆O(SiO₄)₆:Ce³⁺ presents a strong blue emission band at 426 nm which are assigned to 4f⁰5d¹→4f¹ transition of Ce³⁺ ion. Ca₄Y₆O(SiO₄)₆:Eu²⁺ shows green emission under 380 nm radiation excitation, and the peak locates at 527 nm which is mainly due to transitions of Eu²⁺ from 4f⁷ ground state to 4f⁶5d¹ excited state. Under 356 nm excitation, a remarkable energy transfer from Ce³⁺ to Eu²⁺ exists in Ca₄Y₆O(SiO₄)₆, and the result reveals that the mechanism of energy transfer is a resonant type via a nonradiative dipole–dipole interaction. The hues of Ca₄Y₆O(SiO₄)₆:Ce³⁺, Eu²⁺ can be adjusted by the energy transfer from Ce³⁺ to Eu²⁺ ions, and a white emission can be achieved by tuning the ratio of Ce³⁺ to Eu²⁺. The results mean that Ce³⁺ may be the effective sensitizer for Eu²⁺‐doped Ca₄Y₆O(SiO₄)₆.     

Citric based sol-gel synthesis and photoluminescence properties of un-doped and Sm doped Ca3Y2Si3O12 phosphors

The photoluminescent properties of un-doped and Sm³⁺ doped Ca₃Y₂Si₃O₁₂ phosphors were prepared by the citrate sol-gel method. Un-doped sample has shown a strong blue emission, which has its maximum intensity at 389 nm. Among all the observed emission transitions ⁴G_5/2→⁶H_J (J = 5/2, 7/2 & 9/2) of Sm³⁺, the reddish-orange (RO) emission transition ⁴G_5/2→⁶H_7/2 is more prominent, which matches well with the emission wavelength of near UV (n-UV) LED. The reasons for the observance of such prominent visible color emissions from these phosphors have been substantiated appropriately. Besides, structural details of these samples have also been analyzed from the measured XRD, TEM, TG-DTA and FT-IR profiles.     

Spectroscopic investigations on high efficiency deep red-emitting Ca2SiO4:Eu3+ phosphors synthesized from agricultural waste

Europium doped calcium orthosilicate (Ca₂SiO₄) phosphors have been synthesized by the conventional high temperature solid-state reaction method in various concentrations from agricultural waste (egg shell as a CaO and rice husk as a SiO₂). These phosphors structure from X-ray diffraction and morphology from scanning electron microscopy have been examined. Concentration dependent Eu³⁺ ions luminescent properties in Ca₂SiO₄ phosphors have been studied from the excitation, emission and decay curves analysis. The ⁵D₀ → ⁷F_J transitions observed in luminescence spectrum allows to determine the site symmetry of the Eu³⁺ ion. A charge transfer band (CTB) at around 260?nm which is due to the Eu–O interaction in the host along with the 4f – 4f excitation bands due to Eu³⁺ ions in UV and blue regions are observed. The color co-ordinates determined from emission spectra varies with concentrations of Eu³⁺ ions and are found to fall in the red region. The decay curves show single exponential behavior for all concentrations of Eu³⁺ ions (0.01–0.4?mol%) and the lifetimes varied from 2.67 to 2.78?ms. It is worth noting that the present material is found to be far better than many red phosphors synthesized by using agricultural waste as raw materials.